1. Field of the Invention
The present invention relates to a frame structure of a motorcycle including an oil tank integrated into the frame structure.
2. Description of the Background Art
It is known to utilize an inner portion of a vehicle body frame as an oil tank. One example is shown in JP-A-10-71983, wherein respective inner spaces of frame portions are utilized as an oil tank. The oil tank is formed in a main pipe extending rearwardly from a head pipe, a down pipe extending downwardly from the head pipe, as well as a reinforcement pipe connecting the main pipe and the down pipe.
When the oil tank is formed as described above, a rear portion of the main pipe must be hermetically sealed. Further, respective connecting portions must be welded in a liquid-tight manner, and a connector of a gauge or the like must similarly be welded in a liquid-tight manner. When hermetically sealing an end portion of the main pipe, and when the number and length of weld portions requiring liquid-tight performance are increased in this way, much time and labor is needed. Therefore, it is desired to dispense with hermetically sealing of such an end portion of the main pipe and to make the number and lengths of the weld portions requiring liquid-tight performance as small as possible and as short as possible.